[modeleng] Re: sprockets

Thanks Richard - yes, the diameter is a bit flexible & that would be big
enough. To make the problem a little clearer (?) this wheel is wanted for
the drive system under a HO scale canal. One big sprocket at one end under
the turning pool, two smaller ones at the other - ditto, & a couple of idler
wheels to hold everything in shape (coming down the narrow central canal
section) The chain carries a series of rare earth magnets that pull the
barges along thru' the water.

We did have the whole system operating on cable drive with MDF pulleys (on
spring arms for tensioning) but the customer wants to revert to his original
concept of chain drive.

Once we get all this sorted it's back to getting the working lock to do just
that (work). And they wonder why men drink????


> Hi Terry,
>
>     In imperial figures, 240 holes on 19.105" pcd will be exactly .250"
> apart. This is only a 486.41 mm pcd, but you did say approx 500 and 240
> holes at 1.500 degrees sounds a lot easier to me, not that I fancy having
to
> drill them.
>
> ----- Original Message -----
> From: "Terry Lane" <tel@xxxxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Monday, August 30, 2004 11:45 AM
> Subject: [modeleng] Re: sprockets
>
>
> > Thanks Rich - now where did I put that 247 tooth gear wheel to index it
> > with?
> >
> >
> > > Hi there Terry,
> > >
> > > I'd suggest the following (hoping my maths is correct):-
> > >
> > > Guess the number of holes - a good estimate would be to say that the
> > > circumference of your 500mm sprocket is about pi*500mm, which is
1571mm,
> > > and your pitch is 1/4"=6.35mm, which goes into the circumference about
> 247
> > > times.
> > >
> > > Divide 360 degrees with that number - leaving 1.4575 degrees.
> > >
> > > Now draw out a right angled triangle in front of you, with one angle
> very
> > > small.
> > >
> > > Assume that this small angle is half of the 1.4575 degrees (0.7287
> > > degrees), and that the side opposite this angle is half of your pitch
> > > (1/8"=3.175mm).
> > >
> > > The hypotenuse of the triangle should not be the RADIUS that you
should
> > > form the holes on for your sprocket for 495 teeth:-
> > >
> > > hole radius= 3.175mm/ sin 0.7287degrees = 249.633mm
> > >
> > > giving a diameter for your holes to lie on of 499.267mm.
> > >
> > > This doesn't allow for any clearance between the chain rollers and the
> > > sprocket though.
> > >
> > > Hope this is of some use.
> > >
> > >
> > > Yours,
> > >
> > >
> > > Rich.
> > > PS 247 HOLES!!! OUCH!
> > >
> > > On Mon, 30 Aug 2004, Terry Lane wrote:
> > >
> > > > I'm sure the info is somewhere but - have any of you got a quick way
> of
> > > > calculating sprocket cutting. I got a job here that calls for a
> sprocket
> > > > aprox 500mm diameter to drive 1/4" pitch chain. Now OK - the teeth
> gotta
> > be
> > > > one pitch apart, & the holes gotta be pin dia.+?, but how do I
arrive
> at
> > a
> > > > pitch circle for the ring of holes?
> > > >
> > > >
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